Method for forming fin field effect transistor (FINFET) device structure with conductive layer between gate and gate contact

ABSTRACT

A method for forming a FinFET device structure is provided. The method includes forming a fin structure over a substrate and forming a gate dielectric layer over the fin structure. The method also includes forming a gate electrode layer over the gate dielectric layer and forming a source/drain (S/D) structure adjacent to the gate electrode layer. In addition, the method includes forming an S/D contact structure over the S/D structure. The method also includes forming a first conductive layer in direct with the gate electrode layer. A bottom surface of the first conductive layer is lower than a top surface of the gate dielectric layer. The method further includes forming a second conductive layer over the first conductive layer. The gate electrode layer is electrically connected to the second conductive layer by the first conductive layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of pending U.S. patent application Ser.No. 15/821,994, filed Nov. 24, 2017 and entitled “Fin field transistor(FINFET) device structure with conductive layer between gate and gatecontact”, the entirety of which is incorporated by reference herein.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment. Semiconductor devices are typically fabricated bysequentially depositing insulating or dielectric layers, conductivelayers, and semiconductive layers of material over a semiconductorsubstrate, and patterning the various material layers using lithographyto form circuit components and elements thereon. Many integratedcircuits are typically manufactured on a single semiconductor wafer, andindividual dies on the wafer are singulated by sawing between theintegrated circuits along a scribe line. The individual dies aretypically packaged separately, in multi-chip modules, for example, or inother types of packaging.

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as thefin field effect transistor (FinFET). FinFETs are fabricated with a thinvertical “fin” (or fin structure) extending from a substrate. Thechannel of the FinFET is formed in this vertical fin. A gate is providedover the fin. The advantages of a FinFET may include reducing the shortchannel effect and providing a higher current flow.

Although existing FinFET devices and methods of fabricating FinFETdevices have generally been adequate for their intended purpose, theyhave not been entirely satisfactory in all respects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A-1N show perspective representations of various stages offorming a FinFET device structure, in accordance with some embodimentsof the disclosure.

FIGS. 2A-2E show cross-sectional representations of various stages offorming a FinFET device structure shown in FIG. 1J-1N, in accordancewith some embodiments of the disclosure.

FIG. 2E′ shows a cross-sectional representation of a modified FinFETdevice structure, in accordance with some embodiments of the disclosure.

FIG. 2E″ shows a cross-sectional representation of a modified FinFETdevice structure, in accordance with some embodiments of the disclosure.

FIG. 3A is an enlarged cross-sectional representation of region A ofFIG. 2E.

FIGS. 3B-3C show enlarged cross-sectional representations of region B ofFIG. 2E′.

FIGS. 3D-3F show enlarged cross-sectional representations of region C ofFIG. 2E″.

FIG. 4 shows a top-view of FinFET device structure, in accordance withsome embodiments of the disclosure.

FIGS. 5A-5H show perspective representations of various stages offorming a FinFET device structure, in accordance with some embodimentsof the disclosure.

FIG. 5H′ shows a cross-sectional representation of a modified FinFETdevice structure, in accordance with some embodiments of the disclosure.

FIG. 6 shows a top-view of FinFET device structure, in accordance withsome embodiments of the disclosure.

FIGS. 7A-7G show perspective representations of various stages offorming a FinFET device structure, in accordance with some embodimentsof the disclosure.

FIG. 7G′ shows a cross-sectional representation of a modified FinFETdevice structure, in accordance with some embodiments of the disclosure.

FIG. 8 shows a top-view of FinFET device structure, in accordance withsome embodiments of the disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the subject matterprovided. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Some variations of the embodiments are described. Throughout the variousviews and illustrative embodiments, like reference numbers are used todesignate like elements. It should be understood that additionaloperations can be provided before, during, and after the method, andsome of the operations described can be replaced or eliminated for otherembodiments of the method.

The fins may be patterned by any suitable method. For example, the finsmay be patterned using one or more photolithography processes, includingdouble-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in one embodiment,a sacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-alignment process. The sacrificial layeris then removed, and the remaining spacers may then be used to patternthe fins.

Embodiments for forming a fin field effect transistor (FinFET) devicestructure are provided. FIGS. 1A-1N show perspective representations ofvarious stages of forming a FinFET device structure 100 a, in accordancewith some embodiments of the disclosure.

Referring to FIG. 1A, a substrate 102 is provided. The substrate 102 maybe made of silicon or other semiconductor materials. Alternatively oradditionally, the substrate 102 may include other elementarysemiconductor materials such as germanium. In some embodiments, thesubstrate 102 is made of a compound semiconductor such as siliconcarbide, gallium arsenic, indium arsenide, or indium phosphide. In someembodiments, the substrate 102 is made of an alloy semiconductor such assilicon germanium, silicon germanium carbide, gallium arsenic phosphide,or gallium indium phosphide. In some embodiments, the substrate 102includes an epitaxial layer. For example, the substrate 102 has anepitaxial layer overlying a bulk semiconductor.

Afterwards, a dielectric layer 104 and a mask layer 106 are formed overthe substrate 102, and a photoresist layer 108 is formed over the masklayer 106. The photoresist layer 108 is patterned by a patterningprocess. The patterning process includes a photolithography process andan etching process. The photolithography process includes photoresistcoating (e.g., spin-on coating), soft baking, mask aligning, exposure,post-exposure baking, developing the photoresist, rinsing and drying(e.g., hard baking). The etching process may include a dry etchingprocess or a wet etching process.

The dielectric layer 104 is a buffer layer between the substrate 102 andthe mask layer 106. In addition, the dielectric layer 104 is used as astop layer when the mask layer 106 is removed. The dielectric layer 104may be made of silicon oxide. The mask layer 106 may be made of siliconoxide, silicon nitride, silicon oxynitride, or another applicablematerial. In some other embodiments, more than one mask layer 106 isformed over the dielectric layer 104.

The dielectric layer 104 and the mask layer 106 are formed by depositionprocesses, such as a chemical vapor deposition (CVD) process, ahigh-density plasma chemical vapor deposition (HDPCVD) process, aspin-on process, a sputtering process, or another applicable process.

As shown in FIG. 1B, after the photoresist layer 108 is patterned, thedielectric layer 104 and the mask layer 106 are patterned by using thepatterned photoresist layer 108 as a mask, in accordance with someembodiments. As a result, a patterned pad layer 104 and a patterned masklayer 106 are obtained. Afterwards, the patterned photoresist layer 108is removed.

Next, an etching process is performed on the substrate 102 to form a finstructure 110 by using the patterned dielectric layer 104 and thepatterned mask layer 106 as a mask. The etching process may be a dryetching process or a wet etching process.

In some embodiments, the substrate 102 is etched using a dry etchingprocess. The dry etching process includes using a fluorine-based etchantgas, such as SF₆, C_(x)F_(y), NF₃ or a combination thereof. The etchingprocess may be a time-controlled process, and continue until the finstructure 110 reaches a predetermined height. In some other embodiments,the fin structure 110 has a width that gradually increases from the topportion to the lower portion.

As shown in FIG. 1C, after the fin structure 110 is formed, aninsulating layer 112 is formed to cover the fin structure 110 over thesubstrate 102, in accordance with some embodiments.

In some embodiments, the insulating layer 112 is made of silicon oxide,silicon nitride, silicon oxynitride, fluoride-doped silicate glass(FSG), or another low-k dielectric material. The insulating layer 112may be deposited by a chemical vapor deposition (CVD) process, aspin-on-glass process, or another applicable process.

Afterwards, the insulating layer 112 is thinned or planarized to exposethe top surface of the patterned mask layer 106. In some embodiments,the insulating layer 112 is thinned by a chemical mechanical polishing(CMP) process. Afterwards, the patterned dielectric layer 104 and thepatterned mask layer 106 are removed.

Afterwards, as shown in FIG. 1D, a portion of the insulating layer 112is removed to form an isolation structure 114, in accordance with someembodiments. The isolation structure 114 may be a shallow trenchisolation (STI) structure surrounding the fin structure 110. A lowerportion of the fin structure 110 is surrounded by the isolationstructure 114, and an upper portion of the fin structure 110 protrudesfrom the isolation structure 114. In other words, a portion of the finstructure 110 is embedded in the isolation structure 114. The isolationstructure 114 prevents electrical interference and crosstalk.

Afterwards, as shown in FIG. 1E, a dummy gate structure 120 is formedacross the fin structure 110 and extends over the isolation structure114, in accordance with some embodiments. In some embodiments, the dummygate structure 120 includes a dummy gate dielectric layer 116 and adummy gate electrode layer 118 formed over the dummy gate dielectriclayer 116. After the dummy gate structure 120 is formed, the gate spacerlayers 122 are formed on opposite sidewall surfaces of the dummy gatestructure 120. The gate spacer layers 122 may be a single layer ormultiple layers.

In order to improve the speed of the FinFET device structure 100, thegate spacer layers 122 are made of low-k dielectric materials. In someembodiments, the low-k dielectric materials has a dielectric constant (kvalue) is less than 4. Examples of low-k dielectric materials include,but are not limited to, fluorinated silica glass (FSG), carbon dopedsilicon oxide, amorphous fluorinated carbon, parylene,bis-benzocyclobutenes (BCB), or polyimide.

In some other embodiments, the gate spacer layers 122 are made of anextreme low-k (ELK) dielectric material with a dielectric constant (k)less than about 2.5. In some embodiments, ELK dielectric materialsinclude carbon doped silicon oxide, amorphous fluorinated carbon,parylene, bis-benzocyclobutenes (BCB), polytetrafluoroethylene (PTFE)(Teflon), or silicon oxycarbide polymers (SiOC). In some embodiments,ELK dielectric materials include a porous version of an existingdielectric material, such as hydrogen silsesquioxane (HSQ), porousmethyl silsesquioxane (MSQ), porous polyarylether (PAE), porous SiLK, orporous silicon oxide (SiO₂).

Afterwards, source/drain (S/D) structures 124 are formed over the finstructure 110. In some embodiments, portions of the fin structure 110adjacent to the dummy gate structure 120 are recessed to form recessesat two sides of the fin structure 110, and a strained material is grownin the recesses by an epitaxial (epi) process to form the S/D structures124. In addition, the lattice constant of the strained material may bedifferent from the lattice constant of the substrate 102. In someembodiments, the S/D structures 124 include Ge, SiGe, InAs, InGaAs,InSb, GaAs, GaSb, InAlP, InP, or the like.

After the source/drain (S/D) structures 124 are formed, a contact etchstop layer (CESL) (not shown) is formed over the substrate 102, and aninter-layer dielectric (ILD) structure 128 is formed over the contactetch stop layer 126. In some other embodiments, the CESL is made ofsilicon nitride, silicon oxynitride, and/or other applicable materials.The contact etch stop layer may be formed by plasma enhanced CVD,low-pressure CVD, ALD, or other applicable processes.

The ILD structure 128 may include multilayers made of multipledielectric materials, such as silicon oxide, silicon nitride, siliconoxynitride, tetraethoxysilane (TEOS), phosphosilicate glass (PSG),borophosphosilicate glass (BPSG), low-k dielectric material, and/orother applicable dielectric materials. Examples of low-k dielectricmaterials include, but are not limited to, fluorinated silica glass(FSG), carbon doped silicon oxide, amorphous fluorinated carbon,parylene, bis-benzocyclobutenes (BCB), or polyimide. The ILD structure128 may be formed by chemical vapor deposition (CVD), physical vapordeposition, (PVD), atomic layer deposition (ALD), spin-on coating, oranother applicable process.

Afterwards, a polishing process is performed on the ILD structure 128until the top surface of the dummy gate structure 120 is exposed. Insome embodiments, the ILD structure 128 is planarized by a chemicalmechanical polishing (CMP) process.

Afterwards, as shown in FIG. 1F, the dummy gate structure 120 is removedto form a trench 130 in the ILD structure 128, in accordance with someembodiments. The dummy gate dielectric layer 116 and the dummy gateelectrode layer 118 are removed by an etching process, such as a dryetching process or a wet etching process.

Next, as shown in FIG. 1G, a gate structure 140 is formed in the trench130, in accordance with some embodiments. The gate structure 140includes a gate dielectric layer 134 and a gate electrode layer 138.

The gate dielectric layer 134 may be a single layer or multiple layers.The gate dielectric layer 134 is made of silicon oxide (SiOx), siliconnitride (SixNy), silicon oxynitride (SiON), dielectric material(s) withhigh dielectric constant (high-k), or a combination thereof. In someembodiments, the gate dielectric layer 134 is deposited by a plasmaenhanced chemical vapor deposition (PECVD) process or by a spin coatingprocess.

The gate electrode layer 138 is made of conductive material, such asaluminum (Al), copper (Cu), tungsten (W), titanium (Ti), tantalum (Ta),or other applicable materials. In some embodiments, the gate electrodelayer 138 includes a work function layer. The work function layer ismade of metal material, and the metal material may includeN-work-function metal or P-work-function metal. The N-work-functionmetal includes tungsten (W), copper (Cu), titanium (Ti), silver (Ag),aluminum (Al), titanium aluminum alloy (TiAl), titanium aluminum nitride(TiAlN), tantalum carbide (TaC), tantalum carbon nitride (TaCN),tantalum silicon nitride (TaSiN), manganese (Mn), zirconium (Zr) or acombination thereof. The P-work-function metal includes titanium nitride(TiN), tungsten nitride (WN), tantalum nitride (TaN), ruthenium (Ru) ora combination thereof.

The gate electrode layer 138 is formed by a deposition process, such aschemical vapor deposition (CVD), physical vapor deposition (PVD), atomiclayer deposition (ALD), high density plasma CVD (HDPCVD), metal organicCVD (MOCVD), or plasma enhanced CVD (PECVD).

Next, as shown in FIG. 1H, a first dielectric layer 142 is formed overthe gate structure 140 and over the ILD structure 128, in accordancewith some embodiments.

The first dielectric layer 142 may be a single layer or multiple layers.The first dielectric layer 142 is made of silicon oxide (SiOx), siliconnitride (SixNy), silicon oxynitride (SiON), dielectric material(s) withlow dielectric constant (low-k), or combinations thereof. In someembodiments, the first dielectric layer 142 is made of an extreme low-k(ELK) dielectric material with a dielectric constant (k) less than about2.5. In some embodiments, ELK dielectric materials include carbon dopedsilicon oxide, amorphous fluorinated carbon, parylene,bis-benzocyclobutenes (BCB), polytetrafluoroethylene (PTFE) (Teflon), orsilicon oxycarbide polymers (SiOC). In some embodiments, ELK dielectricmaterials include a porous version of an existing dielectric material,such as hydrogen silsesquioxane (HSQ), porous methyl silsesquioxane(MSQ), porous polyarylether (PAE), porous SiLK, or porous silicon oxide(SiO₂). In some embodiments, the dielectric layer 142 is deposited by aplasma enhanced chemical vapor deposition (PECVD) process or by a spincoating process.

Afterwards, as shown in FIG. 1I, a portion of the first dielectric layer142, a portion of the ILD structure 128 are removed to form a trench143, in accordance with some embodiments. As a result, the S/D structure124 is exposed by the trench 143.

Subsequently, as shown in FIG. 1J, a glue layer 144 is formed in thesidewall surfaces of the trench 143, and a metal layer 146 is formed onthe glue layer 144, in accordance with some embodiments. An S/D contactstructure 148 is constructed by the glue layer 144 and the metal layer146. The S/D contact structure 148 is electrically connected to the S/Dstructure 124. A top surface of the S/D contact structure 148 is higherthan a top surface of the gate structure 140.

Afterwards, as shown in FIG. 1K, an etching stop layer 150 and a seconddielectric layer 152 are formed on the first dielectric layer 142, andthen a portion of the second dielectric layer 152, a portion of theetching stop layer 150 and a portion of the first dielectric layer 142are removed to form a first hole 153 above the gate structure 140, inaccordance with some embodiments.

Next, as shown in FIG. 1L, a first conductive layer 154 is selectivelyformed over the gate electrode layer 138, in accordance with someembodiments. More specifically, the first conductive layer 154 is formedin and over the gate electrode layer 138. The first conductive layer 154is configured to reduce the contact resistance between the gateelectrode layer 138 and the second conductive layer 164 (formed later,shown in FIG. 2E). The first conductive layer 154 is a part of the gatecontact structure 166 (shown in FIG. 2E).

It should be noted that as shown in FIG. 2C (the cross-sectional view ofFIG. 1L), the first conductive layer 154 is selectively formed on thegate electrode layer 138 of the gate structure 140, but not formed onthe gate dielectric layer 134. In addition, a portion of the firstconductive layer 154 is embedded in the gate structure 140. The bottomsurface of the first conductive layer 154 is lower than a top surface ofthe gate dielectric layer 134. A top surface of the first conductivelayer 154 is higher than a bottom surface of the S/D contact structure148 and lower than a top surface of the S/D contact structure 148.

The first conductive layer 154 is made of tungsten (W), cobalt (Co),titanium (Ti), aluminum (Al), copper (Cu) or gold (Au). In someembodiments, the first conductive layer 154 is formed by a depositionprocess, such as a chemical vapor deposition (CVD) process, physicalvapor deposition (PVD) process, atomic layer deposition (ALD) process,plating process or another application process. The fabricating methodof the first conductive layer 154 will be described in the FIG. 2C inmore detail.

Afterwards, as shown in FIG. 1M, a portion of the second dielectriclayer 152 and a portion of the etching stop layer 150 are removed toform a second hole 155 above the S/D contact structure 148, inaccordance with some embodiments.

Next, as shown in FIG. 1N, a barrier layer 162 is formed in the firsthole 153 and the second hole 155, and a second conductive layer 164 isformed over the barrier layer 162, in accordance with some embodiments.The first hole 153 is filled with the barrier layer 162 and the secondconductive layer 164, and the gate contact structure 166 is constructedby the first conductive layer 154, the barrier layer 162 and the secondconductive layer 164. The second hole 155 is filled with the barrierlayer 162 and the second conductive layer 164 to form an S/D conductiveplug 168.

The gate contact structure 166 is electrically connected to the gateelectrode layer 138. The S/D conductive plug 168 is directly above theS/D contact structure 148. The S/D conductive plug 168 is electricallyconnected to the S/D structures 124 by the S/D contact structure 148. Insome embodiments, the grain size of the second conductive layer 164 isgreater than the grain size of the first conductive layer 154 to have alower the contact resistance.

In some embodiments, the barrier layer 162 is made of tantalum (Ta),tantalum nitride (TaN), titanium (Ti), titanium nitride (TiN), cobalttungsten (CoW) or another applicable material. In some embodiments, thebarrier layer 162 is formed by a deposition process, such as a chemicalvapor deposition (CVD) process, physical vapor deposition (PVD) process,atomic layer deposition (ALD) process, plating process or anotherapplication process.

In some embodiments, the second conductive layer 164 is made of tungsten(W), cobalt (Co), titanium (Ti), aluminum (Al), copper (Cu), tantalum(Ta), platinum (Pt), molybdenum (Mo), silver (Ag), manganese (Mn),zirconium (Zr), ruthenium (Ru), or another application material. In someembodiments, the second conductive layer 164 is formed by a depositionprocess, such as a chemical vapor deposition (CVD) process, physicalvapor deposition (PVD) process, atomic layer deposition (ALD) process,plating process or another application process. The material of thefirst conductive layer 154 may be the same or different from that of thesecond conductive layer 164.

A first interface is between the first conductive layer 154 and the gateelectrode layer 138, a second interface is between the first conductivelayer 154 and the second conductive layer 164. The first interface has afirst resistance, the second interface has a second resistance, and thesecond resistance is lower than the first resistance. Therefore, thecontact resistance between the gate electrode layer 138 and the secondconductive layer 164 is reduced by forming the first conductive layer154.

It should be noted that as the dimension of the gate structure 140 isgradually decreased, the filling of the gate material into the trench130 becomes difficulty. As a result, there is no enough space to fillthe low-resistance material. Therefore, the first conductive layer 154of the disclosure is formed between the gate electrode layer 138 and thesecond conductive layer 164 to reduce the contact resistance between thegate electrode layer 138 and the second conductive layer 164 of the gatecontact structure 166.

FIGS. 2A-2E show cross-sectional representations of various stages offorming a FinFET device structure 100 a shown in FIG. 1J-1N, inaccordance with some embodiments of the disclosure. FIG. 2A is across-sectional representation taken along the II′ line of FIG. 1J.

As shown in FIG. 2A, the glue layer 144 is formed in the sidewallsurfaces of the trench 143, and the metal layer 146 is formed on theglue layer 144, in accordance with some embodiments. The S/D contactstructure 148 is constructed by the glue layer 144 and the metal layer146. The S/D contact structure 148 is electrically connected to the S/Dstructure 124.

Next, as shown in FIG. 2B, the etching stop layer 150 and the seconddielectric layer 152 are formed on the first dielectric layer 142, and afirst hole 153 directly above the gate structure 140 is formed byremoving a portion of the second dielectric layer 152, a portion of theetching stop layer 150 and a portion of the first dielectric layer 142,in accordance with some embodiments. The top surface of the gateelectrode layer 138 is exposed by the first hole 153. The first hole 153has a tapered width from top to bottom. In other words, the first hole153 has a top width and a bottom width, and the top width is greaterthan the bottom width.

Afterwards, as shown in FIG. 2C, the first conductive layer 154 isselectively formed over the gate electrode layer 138, in accordance withsome embodiments. A portion of the first conductive layer 154 isembedded in the gate electrode layer 138. A portion of the firstconductive layer 154 is extended above the top surface of the gatedielectric layer 134. The bottom surface of the first conductive layer154 is lower than the top surface of the gate dielectric layer 134. Thefirst conductive layer 154 is configured to reduce the contactresistance between the gate electrode layer 138 and the secondconductive layer of the gate contact structure 166 (formed later).

Before forming the first conductive layer 154, the top surface of thegate electrode layer 138 is exposed by the first hole 153. In someembodiments, a surface treatment process is performed on the top surfaceof the gate electrode layer 138 to facilitate the following depositionprocess for forming the first conductive layer 154. In some embodiments,the surface treatment process is performed by using oxygen (O₂) plasma,nitrogen (N₂) and oxygen (O₂) plasma, or ammonia (NH₃) plasma.

In some embodiments, the native oxide is formed on the top surface ofthe gate electrode layer 138, but the native oxide is not distributeduniformly. In order to thicken the native oxide layer, in someembodiments, the oxygen (O₂) plasma is used to form a uniform oxidelayer on the overall top surface of the gate electrode layer 138.Afterwards, the uniform oxide layer is removed and replaced by the firstconductive layer 154 to form a uniform first conductive layer 154.

In some other embodiments, the nitrogen (N₂) plasma or the ammonia (NH₃)plasma is used. The nitrogen (N₂) plasma or the ammonia (NH₃) plasma isused to break the chemical bonds of the gate electrode layer 138 and toform new chemical bonds with the first conductive layer 154.

In some embodiments, the surface treatment process is operated at atemperature in a range from about 150 degrees to about 350 degrees. Insome embodiments, the surface treatment process is operated at apressure in a range from about 50 mtorr to about 4000 mtorr. In someembodiments, the surface treatment process is operated at RF power in arange from about 50 W to about 5000 W. In some embodiments, the gas flowin the surface treatment process is in a range from about 100 sccm toabout 10000 sccm. In some embodiments, the surface treatment process isoperated for a period of time in a range from about 10 seconds to about50 seconds.

After the surface treatment process, a deposition process is performedon the gate electrode layer 138 to form the first conductive layer 154.During the deposition process, the native oxide is removed and replacedby the first conductive layer 154, and therefore a portion of the firstconductive layer 154 is embedded in the gate structure 140. Thedeposition is selectively on the gate electrode layer 138, and not onthe gate dielectric layer 134.

In some embodiments, the deposition process is an ALD process. The ALDprocess is performed by using a precursor gas. The precursor gas mayinclude a compound with metal element and halogen element. The compoundmay be tungsten chloride (WCl₅), tungsten fluoride (WF₆), titaniumchloride (TiCl₄) or another applicable material. Furthermore, theprecursor gas may further include hydrogen (H₂) or silane (SiH₄). Insome embodiments, the precursor gas includes tungsten chloride (WCl₅)and hydrogen (H₂). In some other embodiments, the precursor gas includestungsten fluoride (WF₆) and silane (SiH₄).

In some embodiments, the deposition process is operated at a temperaturein a range from about 400 degrees to about 520 degrees. In someembodiments, the deposition process is operated at a pressure in a rangefrom about 5 torr to about 50 torr. In some embodiments, the depositionprocess is operated for a period of time in a range from about 10minutes to about 120 minutes.

Next, as shown in FIG. 2D, the second hole 155 directly above the S/Dcontact structure 148 is formed by removing a portion of the seconddielectric layer 152 and a portion of the etching stop layer 150, inaccordance with some embodiments. The first hole 153 is deeper than thesecond hole 155. The top surface of the S/D contact structure 148 isexposed by the second hole 155. The second hole 155 has a tapered widthfrom top to bottom.

Afterwards, as shown in FIG. 2E, the first hole 153 is filled with thebarrier layer 162 and the second conductive layer 164, and the secondhole 155 is filled with the barrier layer 162 and the second conductivelayer 164 to form the S/D conductive plug 168, in accordance with someembodiments.

The gate structure 140 has a height H₁, and the first conductive layer154 has a second height H₂. The first dielectric layer 142 has a thirdheight H₃. In some embodiments, the first height H₁ is in a range fromabout 10 nm to about 35 nm. In some embodiments, the second height H₂ isin a range from about 2 nm to about 5 nm. In some embodiments, the thirdheight H₃ is in a range from about 5 nm to about 25 nm.

It should be noted that the contact resistance between the secondconductive layer 164 and the first conductive layer 154 is lower thanthe contact resistance between the first conductive layer 154 and thegate electrode layer 138 of the gate structure 140. Therefore, thecontact resistance between the second conductive layer 164 of the gatecontact structure 166 and the gate electrode layer 138 is greatlyreduced by interposing the first conductive layer 154. When the contactresistance between the second conductive layer 164 of the gate contactstructure 166 and the gate electrode layer 138 is reduced, theperformance of the FinFET device structure 100 a is improved.

Furthermore, the native oxide layer formed on the gate electrode layer138 is reduced or eliminated by forming the first conductive layer 154.In addition, the aspect ratio of the first hole 153 for filling thesecond conductive layer 164 is reduced due to formation of the firstconductive layer 154.

FIG. 2E′ shows a cross-sectional representation of a modified FinFETdevice structure 100 b, in accordance with some embodiments of thedisclosure. The FinFET device structure of FIG. 2E′ is similar to theFinFET device structure of FIG. 2E, the difference between FIGS. 2E and2E′ is that the gate electrode layer 138 includes a first layer 138 aand a second layer 138 b. The first conductive layer 154 is formed onthe first layer 138 a and the second layer 138 b of the gate electrodelayer.

The first layer 138 a of the gate electrode layer 138 and the secondlayer 138 b of the gate electrode layer 138 are made of different workfunction materials. The work function material may includeN-work-function metal or P-work-function metal. The N-work-functionmetal includes tungsten (W), copper (Cu), titanium (Ti), silver (Ag),aluminum (Al), titanium aluminum alloy (TiAl), titanium aluminum nitride(TiAlN), tantalum carbide (TaC), tantalum carbon nitride (TaCN),tantalum silicon nitride (TaSiN), manganese (Mn), zirconium (Zr) or acombination thereof. The P-work-function metal includes titanium nitride(TiN), tungsten nitride (WN), tantalum nitride (TaN), ruthenium (Ru) ora combination thereof.

FIG. 2E″ shows a cross-sectional representation of a modified FinFETdevice structure 100 c, in accordance with some embodiments of thedisclosure. The FinFET device structure of FIG. 2E″ is similar to theFinFET device structure of FIG. 2E, the difference between FIGS. 2E and2E″ is that the gate electrode layer 138 includes a first layer 138 a, asecond layer 138 b and a third layer 138 c in FIG. 2E″. The firstconductive layer 154 is formed on the first layer 138 a, the secondlayer 138 b and the third layer 138 c of the gate electrode layer 138.The first layer 138 a, the second layer 138 b and the third layer 138 care made of different materials.

FIG. 3A is an enlarged cross-sectional representation of region A ofFIG. 2E. The first conductive layer 154 is directly above the gateelectrode layer 138. The first conductive layer 154 is not formed on thegate dielectric layer 134 and the gate spacer layers 122. A portion ofthe first conducive layer 154 is formed in the gate structure 140.

FIGS. 3B-3C show enlarged cross-sectional representations of region B ofFIG. 2E′. As shown in FIG. 3B, the first conductive layer 154 is formedon the first layer 138 a and the second layer 138 b of the gateelectrode layer 138.

As shown in FIG. 3C, the first conductive layer 154 is formed on thefirst layer 138 a and the second layer 138 b of the gate electrode layer138. The first conductive layer 154 includes an embedded portion whichis below a top surface of the gate dielectric layer 134, and theembedded portion has a protrusion portion 157 extending away from thetop surface of the gate dielectric layer 134. The protrusion portion 157penetrates into the first layer 138 a of the gate electrode layer 138,but not into the second layer 138 b and the gate dielectric layer 134.Since the material of the first layer 138 a of the gate electrode layer138 is different from the material of the second layer 138 b, the depthsof the first portion of the native oxide layer on the first layer 138 aof the gate electrode layer 138 is different than the depths of thesecond portion of the native oxide layer on the second layer 138 b. Thenative oxide layer with different depths is replaced by the firstconductive layer 154, and therefore the first conductive layer 154 isformed to have different depths. As a result, the first conductive layer154 has a uneven top surface and uneven bottom surface.

FIGS. 3D-3F show enlarged cross-sectional representations of region C ofFIG. 2E″. As mentioned above, the gate structure 140 includes the gatedielectric layer 134, the first layer 138 a, the second layer 138 b andthe third layer 138 c of the gate electrode layer 138.

As shown in FIG. 3D, the first conductive layer 154 is formed on thefirst layer 138 a, the second function layer 138 b and the third layer138 c of the gate electrode layer 138. The outer sidewall surface of thethird layer 138 c of the gate electrode layer is substantially alignedwith the outer sidewall surface of the first conductive layer 154.

As shown in FIG. 3E, the protrusion portion 157 penetrates into the gateelectrode layer 138. More specifically, there are two protrusionportions 157 a, 157 b which penetrates into the second layer 138 b.

FIG. 4 shows a top-view of FinFET device structure 100 a, in accordancewith some embodiments of the disclosure. The first conductive layer 154is formed on the gate structure 140, and the second conductive layer 164is formed on the first conductive layer 154. The top view of the firstconductive layer 154 may have various shapes, such as circular, square,rectangle or other shapes.

The gate structure 140 has a first width W₁ (also called the gatelength). The first conductive layer 154 has a second width W2. The topsurface of the second conductive layer 164 has a third width W₃. The S/Dconductive plug 168 has a fourth width W₄. The first width W₁ is greaterthan the second width W₂. The third width W₃ is greater than the secondwidth W₂, and the first width W₁ is greater than the third width W₃. Thefourth width W₄ is greater than the third width W₃. In some embodiments,the first width W₁ (also called gate length) of the gate structure 140is in a range from about 13 nm to about 28 nm. In some embodiments, thesecond width W₂ of the first conductive layer 154 is in a range fromabout 10 nm to about 16 nm. In some embodiments, the fourth width W₄ isin a range from about 12 nm to about 18 nm.

FIGS. 5A-5H show perspective representations of various stages offorming a FinFET device structure 200 a, in accordance with someembodiments of the disclosure. Some processes and materials used to formthe FinFET device structure 200 a are similar to, or the same as, thoseused to form the FinFET device structure 100 a and are not repeatedherein.

As shown in FIG. 5A, the first hole 153 is formed on the gate structure140. The top surface of the gate electrode layer 138 is exposed by thefirst hole 153. The first hole 153 has a tapered width from top tobottom.

Afterwards, as shown in FIG. 5B, the first conductive layer 154 isformed on sidewall surfaces and the bottom surface of the first hole153, in accordance with some embodiments of the disclosure. The firstconductive layer 154 is conformally formed on the top surface of thesecond dielectric layer 152 and sidewall surfaces of the first hole 153.

Next, as shown in FIG. 5C, a photoresist (PR) layer 156 is formed on thefirst conductive layer 154 and in a portion of the first hole 153, inaccordance with some embodiments of the disclosure. The PR layer 156 isused as a protection layer to protect the first conductive layer 154from being etched in the following process.

Subsequently, as shown in FIG. 5D, a portion of the first conductivelayer 154 is removed, in accordance with some embodiments of thedisclosure. The portion of the first conductive layer 154 above thesecond dielectric layer 152 is removed, but another portion which isprotected by the PR layer 156 is not removed. The remaining firstconductive layer 154 has a U-shaped structure, and the PR layer 156 isin the middle portion of the U-shaped structure.

Next, as shown in FIG. 5E, the PR layer 156 is removed, in accordancewith some embodiments of the disclosure. As a result, the U-shaped firstconductive layer 154 is exposed. It should be noted that the thicknessof the sidewall portion of the U-shaped first conductive layer 154 isthinner than the thickness of the bottom portion of the U-shaped firstconductive layer 154.

Afterwards, as shown in FIG. 5F, a portion of the first conductive layer154 is removed, in accordance with some embodiments of the disclosure.Since the thickness of the sidewall portion of the U-shaped firstconductive layer 154 is thinner than the thickness of the bottom portionof the U-shaped first conductive layer 154, the sidewall portion isremoved but the bottom portion is still remaining. As a result, thefirst conductive layer 154 is formed on the gate electrode layer 138.

Next, as shown in FIG. 5G, the second hole 155 is formed on the S/Dcontact structure 148, in accordance with some embodiments of thedisclosure.

Afterwards, as shown in FIG. 5H, the barrier layer 162 is formed in thefirst hole 153 and the second hole 155, and the second conductive layer164 is formed over the barrier layer 162, in accordance with someembodiments. The top portion of the gate contact structure 166 is formedby filling the first hole 153 with the barrier layer 162 and the secondconductive layer 164. The S/D conductive plug 168 is formed by fillingthe second hole 155 with the barrier layer 162 and the second conductivelayer 164.

The second conductive layer 164 is electrically connected to the gateelectrode layer 138 of the gate structure 140 by the first conductivelayer 154. The S/D conductive plug 168 is directly above the S/D contactstructure 148. The S/D conductive plug 168 is electrically connected tothe S/D structures 124 by the S/D contact structure 148.

FIG. 5H′ shows a cross-sectional representation of a modified FinFETdevice structure 200 b, in accordance with some embodiments of thedisclosure. The FinFET device structure of FIG. 5H′ is similar to theFinFET device structure of FIG. 5H, the difference between FIGS. 5H and5H′ is that the gate electrode layer 138 includes a first layer 138 aand a second layer 138 b. The first conductive layer 154 is formed onthe first layer 138 a and the second layer 138 b.

FIG. 6 shows a top-view of FinFET device structure 200 a or 200 b, inaccordance with some embodiments of the disclosure. The first conductivelayer 154 is between the gate structure 140 and the second conductivelayer 164. The width of the first conductive layer 154 is smaller thanthe width of the gate structure 140. The S/D conductive plug 168 isformed on the S/D contact structure 148. The width of the S/D conductiveplug 168 is greater than the width of the S/D contact structure 148.

FIGS. 7A-7G show perspective representations of various stages offorming a FinFET device structure 300 a, in accordance with someembodiments of the disclosure. Some processes and materials used to formthe FinFET device structure 300 a are similar to, or the same as, thoseused to form the FinFET device structure 100 a and are not repeatedherein.

As shown in FIG. 7A, the first hole 153 is formed on the gate structure140. The top surface of the gate electrode layer 138 is exposed by thefirst hole 153. The first hole 153 has a tapered width from top tobottom.

Afterwards, as shown in FIG. 7B, the first conductive layer 154 isformed on sidewall surfaces and the bottom surface of the first hole153, in accordance with some embodiments of the disclosure. The firstconductive layer 154 includes a first layer 154 a and a second layer 154b formed on the first layer 154 a. The first layer 154 a and the secondlayer 154 b are made of different materials. In some embodiments, thefirst layer 154 a is made of titanium (Ti), and the second layer 154 bis made of titanium nitride (TiN). The titanium (Ti) can capture theoxygen in the top surface of the gate electrode layer 138 to formtitanium oxide (TiOx) to reduce the contact resistance between the firstlayer 154 a and the gate electrode layer 138.

Next, as shown in FIG. 7C, the photoresist (PR) layer 156 is formed onthe first conductive layer 154 and in a portion of the first hole 153,in accordance with some embodiments of the disclosure. The PR layer 156is used as a protection layer to protect the first conductive layer 154from being etched in the following process.

Subsequently, as shown in FIG. 7D, a portion of the first conductivelayer 154 is removed, in accordance with some embodiments of thedisclosure. The portion of the first conductive layer 154 above thesecond dielectric layer 152 is removed, but another portion which isprotected by the PR layer 156 is not removed. More specifically, thefirst layer 154 a and the second layer 154 b each have a U-shapedstructure, and the PR layer 156 is in the middle portion of the U-shapedstructure.

Afterwards, as shown in FIG. 7E, the PR layer 156 is removed, inaccordance with some embodiments of the disclosure. As a result, theU-shaped conductive layer 154 is exposed. The second layer 154 b isembedded in the first layer 154 a. The second layer 154 b is surroundedby the first layer 154 a.

Subsequently, as shown in FIG. 7F, the second hole 155 is formed on theS/D contact structure 148, in accordance with some embodiments of thedisclosure.

Next, as shown in FIG. 7G, the second conductive layer 164 is formed onthe first conductive layer 154, and the S/D conductive plug 168 isformed on the S/D contact structure 148, in accordance with someembodiments of the disclosure.

FIG. 7G′ shows a cross-sectional representation of a modified FinFETdevice structure 300 b, in accordance with some embodiments of thedisclosure. The FinFET device structure of FIG. 7G′ is similar to theFinFET device structure of FIG. 7G, the difference between FIGS. 7G and7G′ is that the gate electrode layer 138 includes a first layer 138 aand a second layer 138 b. The first conductive layer 154 is formed onthe first layer 138 a and the second layer 138 b.

FIG. 8 shows a top-view of FinFET device structure 300 a or 300 b, inaccordance with some embodiments of the disclosure. The first conductivelayer 154 including the first layer 154 a and the second layer 154 b isbetween the gate structure 140 and the second conductive layer 164. Thefirst layer 154 a has a ring-shaped structure in a top-view, and thesecond layer 154 b is surrounded by the first layer 154 a.

In the first embodiments, the first conductive layer 154 is selectivelyformed on the gate electrode layer and/or the work function layer. Aportion of the first conductive layer 154 is embedded in the gatestructure 140. The bottom surface of the first conductive layer 154 islower than the top surface of the gate dielectric layer 1534 and the topsurface of the gate spacer layers 122. In some embodiments, the firstconductive layer 154 has a protrusion portion penetrate into the gateelectrode layer (or the work function layer).

In the second embodiment, the overall conductive layer 154 is over thegate structure 140. In the third embodiment, the first conductive layer154 includes a U-shaped first layer and a second layer surrounding thefirst layer. The first conductive layer 154 is sandwiched between thegate electrode layer 138 and the second conductive layer to reduce thecontact resistance.

Embodiments for forming a FinFET device structure and method forformation the same are provided. The FinFET device structure includes agate structure formed over a fin structure, and a conductive layer overthe gate structure. The gate structure includes a gate dielectric layerand a gate electrode layer (or the work function layer). The firstconductive layer is formed over the gate electrode layer, but not formedon the gate dielectric layer. A second conductive layer is formed overthe first conductive layer. A gate contact structure is constructed bythe first conductive layer, a barrier layer and the second conductivelayer. The contact resistance between the gate electrode layer of thegate structure and the second conductive layer is improved by theformation of the first conductive layer. Furthermore, the native oxidelayer formed on the gate electrode layer is reduced or eliminated by theformation of the first conductive layer. In addition, the aspect ratioof the first hole for filling the second conductive layer is reduced dueto the formation of the first conductive layer. Therefore, theperformance of the FinFET device structure is reduced.

In some embodiments, a method for forming a FinFET device structure isprovided. The method includes forming a fin structure over a substrateand forming a gate dielectric layer over the fin structure. The methodalso includes forming a gate electrode layer over the gate dielectriclayer and forming a source/drain (S/D) structure adjacent to the gateelectrode layer. In addition, the method includes forming an S/D contactstructure over the S/D structure. The method also includes forming afirst conductive layer in direct with the gate electrode layer. A bottomsurface of the first conductive layer is lower than a top surface of thegate dielectric layer. The method further includes forming a secondconductive layer over the first conductive layer. The gate electrodelayer is electrically connected to the second conductive layer by thefirst conductive layer.

In some embodiments, a method for forming a FinFET device structure isprovided. The method includes forming gate spacers over a fin structurethat is formed over a substrate. The method also includes successivelyforming a gate dielectric layer and a gate electrode layer over the finstructure, so that the gate spacer layers formed over opposite sidewallsurfaces of the gate electrode layer and separated from the sidewallsurfaces of gate electrode layer by the gate dielectric layer. Themethod further includes forming a first dielectric layer formed over thegate electrode layer. In addition, the method includes etching the firstdielectric layer to forming a hole exposing the gate electrode layer andextending the hole by recessing the exposed gate electrode layer. Themethod also includes forming a gate contact structure in the extendedhole. The gate contact structure includes a first conductive layerincluding a first portion in the first dielectric layer and a secondportion extending from the first portion and in direct contact a topsurface of the gate electrode layer. The gate contact structure alsoincludes a barrier layer formed over the first conductive layer in thefirst dielectric layer.

In some embodiments, a method for forming a FinFET device structure isprovided. The method includes forming a gate structure over a finstructure that is formed over a substrate and forming a source/drain(S/D) structure over the fin structure and adjacent to the gatestructure. The method also includes forming a dielectric layer over thegate structure and the source/drain (S/D) structure and forming asource/drain (S/D) contact structure in the dielectric layer andadjacent to the gate structure. In addition, the method includessuccessively forming a first conductive layer and a second conductivelayer in the dielectric layer and over the gate structure. A top surfaceof S/D contact structure is higher than a top surface of the firstconductive layer and lower than a top surface of the second conductivelayer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for forming a fin field effecttransistor (FinFET) device structure, comprising: forming a finstructure over a substrate; forming a gate dielectric layer over the finstructure; forming a gate electrode layer over the gate dielectriclayer; forming a source/drain (S/D) structure adjacent to the gateelectrode layer; forming an S/D contact structure over the S/Dstructure; after the S/D contact structure is formed, forming a firstconductive layer in direct contact with the gate electrode layer,wherein a bottom surface of the first conductive layer is lower than atop surface of the gate dielectric layer; forming a barrier layer overthe first conductive layer, wherein a width of a bottom surface of thebarrier layer is equal to a width of a top surface of the firstconductive layer; and forming a second conductive layer over the firstconductive layer, wherein the gate electrode layer is electricallyconnected to the second conductive layer by the first conductive layer.2. The method for forming the fin field effect transistor (FinFET)device structure as claimed in claim 1, wherein forming the firstconductive layer on the gate electrode layer comprises: performing asurface treatment process on the top surface of the gate electrodelayer; and selectively forming a conductive material on the top surfaceof the gate electrode layer, wherein the conductive material is formedon the gate electrode layer, and is formed indirectly on the gatedielectric layer.
 3. The method for forming the fin field effecttransistor (FinFET) device structure as claimed in claim 2, wherein thesurface treatment process is performed by using oxygen (O₂) plasma,nitrogen (N₂) plasma, or ammonia (NH₃) plasma.
 4. The method for formingthe fin field effect transistor (FinFET) device structure as claimed inclaim 1, wherein forming the gate dielectric layer over the finstructure and forming the gate electrode layer over the gate dielectriclayer comprises: forming a dummy gate structure over the fin structure;forming a pair of gate spacer layers on opposite sidewall surfaces ofthe dummy gate structure; removing the dummy gate structure to form atrench in the gate spacer layers; filling the gate dielectric layer inthe trench; and forming the gate electrode layer on the gate dielectriclayer.
 5. The method for forming the fin field effect transistor(FinFET) device structure as claimed in claim 1, further comprising:forming an S/D conductive plug over the S/D contact structure, whereinthe S/D conductive plug is electrically connected to the S/D contactstructure.
 6. The method for forming the fin field effect transistor(FinFET) device structure as claimed in claim 1, wherein the top surfaceof the first conductive layer is higher than a bottom surface of the S/Dcontact structure and lower than a top surface of the S/D contactstructure.
 7. The method for forming the fin field effect transistor(FinFET) device structure as claimed in claim 1, wherein forming thebarrier layer over the first conductive layer is performed after formingthe first conductive layer in direct with the gate electrode layer, sothat the barrier layer is between the second conductive layer and thefirst conductive layer, wherein the second conductive layer issurrounded by the barrier layer.
 8. A method for forming a fin fieldeffect transistor (FinFET) device structure, comprising: forming gatespacers over a fin structure that is formed over a substrate; forming agate dielectric layer over the fin structure; forming a gate electrodelayer over the gate dielectric layer; forming a source/drain (S/D)structure adjacent to the gate electrode layer; forming an S/D contactstructure over the S/D structure; after the S/D contact structure isformed, forming a first conductive layer in direct contact with the gateelectrode layer, wherein a first portion of the first conductive layerprotrudes from a top of the gate spacer and a second portion of thefirst conductive layer is surrounded by the gate dielectric layer;forming a barrier layer over the first conductive layer in a firstdielectric layer, wherein a width of a top of the barrier layer isgreater than a width of a top surface of the first conductive layer. 9.The method for forming the fin field effect transistor (FinFET) devicestructure as claimed in claim 8, further comprising: forming a secondconductive layer over the barrier layer, wherein the second conductivelayer is electrically connected to the gate electrode layer by the firstconductive layer.
 10. The method for forming the fin field effecttransistor (FinFET) device structure as claimed in claim 9, wherein agrain size of the second conductive layer is greater than a grain sizeof the first conductive layer.
 11. The method for forming the fin fieldeffect transistor (FinFET) device structure as claimed in claim 8,further comprising: forming the first dielectric layer formed over thegate electrode layer; etching the first dielectric layer to forming ahole exposing the gate electrode layer; and extending the hole byrecessing the exposed gate electrode layer.
 12. The method for formingthe fin field effect transistor (FinFET) device structure as claimed inclaim 11, further comprising: successively forming an etching stop layerand a second dielectric layer over the first dielectric layer beforeforming the hole exposing the gate electrode layer; and successivelyetching the second dielectric layer and the etching stop layer to exposethe hole in the first dielectric layer, wherein the barrier layerthrough the second dielectric layer, the etching stop layer, and thefirst dielectric layer.
 13. The method for forming the fin field effecttransistor (FinFET) device structure as claimed in claim 11, wherein thegate electrode layer comprising a native oxide thereon and extending thehole by recessing the exposed gate electrode layer comprises: removingthe native oxide by a surface treatment process.
 14. The method forforming the fin field effect transistor (FinFET) device structure asclaimed in claim 13, wherein the surface treatment process is performedby using oxygen (O₂) plasma.
 15. The method for forming the fin fieldeffect transistor (FinFET) device structure as claimed in claim 8,wherein the gate electrode layer comprises a first layer and a secondlayer surrounding the first layer, and the first conductive layercomprises a protrusion portion which is extended into the first layer.16. A method for forming a fin field effect transistor (FinFET) devicestructure, comprising: forming a gate structure over a fin structurethat is formed over a substrate; forming a source/drain (S/D) structureover the fin structure and adjacent to the gate structure; forming adielectric layer over the gate structure and the source/drain (S/D)structure; forming a source/drain (S/D) contact structure in thedielectric layer and adjacent to the gate structure; after the S/Dcontact structure is formed, forming a first conductive layer and asecond conductive layer in the dielectric layer and over the gatestructure; and forming a barrier layer over the first conductive layerbefore forming the second conductive layer, wherein the barrier layervertically overlaps sidewalls of the first conductive layer.
 17. Themethod for forming the fin field effect transistor (FinFET) devicestructure as claimed in claim 16, wherein forming the first conductivelayer comprises: etching the dielectric layer to form a hole exposingthe gate structure; forming a first layer in the hole and over the gatestructure, wherein the first layer has a U-shaped structure; and forminga second layer in the first layer, so that the second layer is embeddedin the first layer.
 18. The method for forming the fin field effecttransistor (FinFET) device structure as claimed in claim 17, wherein afirst interface between the barrier layer and the dielectric layer isaligned with a second interface between the first layer and thedielectric layer, and wherein the first interface and the secondinterface extend along the same direction.
 19. The method for formingthe fin field effect transistor (FinFET) device structure as claimed inclaim 16, wherein the gate structure has a first width, a top surface ofthe first conductive layer has a second width, a top surface of thesecond conductive layer has a third width, the first width is greaterthan the second width, and the third width is greater than the secondwidth.
 20. The method for forming the fin field effect transistor(FinFET) device structure as claimed in claim 16, wherein a bottomsurface of the first conductive layer is not higher than a top surfaceof the gate dielectric layer.